Transcatheter aortic valve replacement (TAVR) has emerged as a treatment option for patients with severe symptomatic aortic stenosis at high risk for surgical aortic valve replacement (SAVR). In order to select appropriate TAVR prosthesis for optimal outcome, non-invasive imaging techniques, such as CT and 3D echocardiography, are routinely performed to characterize the aortic root anatomy and ensure accurate annulus sizing. However, due to the sutureless nature of TAVR procedure, the occurrence of mild or more paravalvular leak (PVL) after TAVR is higher than after surgical aortic valve replacement (SAVR), affecting 26-67% patients. Multicenter studies have found moderate to severe post-TAVR PVL to be an independent risk factor for increased short- and long-term mortality. Although a number of PVL predictors have been proposed, there is no broad consensus on how the current practice of patient screening and prosthesis selection can be refined in order to reduce PVL.
3D printing, or additive manufacturing (AM), refers to the layer-by-layer fabrication of objects in an additive process from CAD models. It features a high ability for customization, high geometrical complexity and cost effectiveness in some cases with low production volume, which is perfectly suited for biomedical applications like prosthetics.
Although the uniaxial tensile properties of phantom materials can be close to soft tissues at small strain (<3%) range, the creep tendency, an inherent characteristic of polymers, makes them behave quite differently than the soft tissues under larger deformation. For tissue-mimicking phantoms, the strain range-of-interest is normally the working strain range of the tissue. Soft tissues typically exhibit a strain-stiffening behavior initially, which is represented by a convex stress-strain curve in the beginning. As the strain increases, the curve changes from convex to concave, which indicates yielding of the material. In contrast, the stress-strain curve of a polymer material is usually concave from the beginning, indicating a strain-softening feature. Even though the initial Young's modulus (elastic modulus) of a polymeric phantom can be designed to match the Young's modulus of the real tissue, the mechanical behavior of the phantom will deviate from the real tissue at higher strain levels.
Since creep is an intrinsic property of polymeric materials, single-material polymer 3D printing is generally not capable of generating phantoms that are mechanically accurate in the strain range-of-interest. Recent advances in 3D printed metamaterials provides new insight to this challenge. Metamaterials were first introduced as novel electromagnetic (EM) materials and their characteristic structural length is one or more orders smaller than the EM wavelengths. Since then, the concept of metamaterials has been extended to include any materials whose effective properties are delivered by its structure rather than the bulk behavior of the base materials that composed it. In other words, the geometry, size, orientation and arrangement of the unit cells of metamaterials grant them the desired properties. Here, the value of the “metamaterial” concept is the idea of constructing artificial models of tissue with heterogeneous microstructures that, although difficult to do conventionally, can be printed using additive manufacturing.
To improve patient outcomes following TAVR procedures, an improved modeling technique is needed to better predict the interaction of the TAVR prosthesis with the human aorta, and thereby predict surgical outcomes, such as the occurrence of PVL. However, as would be understood by a person of ordinary skill in the art, the present disclosed technology is not so limited. Indeed, the techniques described herein can be applied to other biological tissues and organs, both human and animal.